如前所述,如果没有剩余写入程序,则命名管道读取器将收到EOF。

然而,我发现@JimB的解决方案不是最优的:

2. 如果重新启动,平均会丢失50ms的数据。再说一次,没有什么好理由。
3. io.CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) 会是更好的解决方案,伊姆霍。但这甚至没有必要,因为 io.Copy

我的方法

github.com/rjeczalik/notify 可以用于访问我们感兴趣的事件,因为写入事件在大多数重要操作系统上跨平台工作。我们感兴趣的另一个事件是删除命名管道,因为我们将没有任何可读取的内容。

因此,我的解决方案是:

package main

import (
    "flag"
    "io"
    "log"
    "os"

    "github.com/rjeczalik/notify"
)

const (
    MAX_CONCURRENT_WRITERS = 5
)

var (
    pipePath string
    filePath string
)

func init() {
    flag.StringVar(&pipePath, "pipe", "", "/path/to/named_pipe to read from")
    flag.StringVar(&filePath, "file", "out.txt", "/path/to/output file")
    log.SetOutput(os.Stderr)
}

func main() {
    flag.Parse()

    var p, f *os.File
    var err error
    var e notify.EventInfo

    // The usual stuff: checking wether the named pipe exists etc
    if p, err = os.Open(pipePath); os.IsNotExist(err) {
        log.Fatalf("Named pipe '%s' does not exist", pipePath)
    } else if os.IsPermission(err) {
        log.Fatalf("Insufficient permissions to read named pipe '%s': %s", pipePath, err)
    } else if err != nil {
        log.Fatalf("Error while opening named pipe '%s': %s", pipePath, err)
    }
    // Yep, there and readable. Close the file handle on exit
    defer p.Close()

    // Do the same for the output file
    if f, err = os.OpenFile(filePath, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600); os.IsNotExist(err) {
        log.Fatalf("File '%s' does not exist", filePath)
    } else if os.IsPermission(err) {
        log.Fatalf("Insufficient permissions to open/create file '%s' for appending: %s", filePath, err)
    } else if err != nil {
        log.Fatalf("Error while opening file '%s' for writing: %err", filePath, err)
    }
    // Again, close the filehandle on exit
    defer f.Close()

    // Here is where it happens. We create a buffered channel for events which might happen
    // on the file. The reason why we make it buffered to the number of expected concurrent writers
    // is that if all writers would (theoretically) write at once or at least pretty close
    // to each other, it might happen that we loose event. This is due to the underlying implementations
    // not because of go.
    c := make(chan notify.EventInfo, MAX_CONCURRENT_WRITERS)

    // Here we tell notify to watch out named pipe for events, Write and Remove events
    // specifically. We watch for remove events, too, as this removes the file handle we
    // read from, making reads impossible
    notify.Watch(pipePath, c, notify.Write|notify.Remove)

    // We start an infinite loop...
    for {
        // ...waiting for an event to be passed.
        e = <-c

        switch e.Event() {

        case notify.Write:
            // If it a a write event, we copy the content of the named pipe to
            // our output file and wait for the next event to happen.
            // Note that this is idempotent: Even if we have huge writes by multiple
            // writers on the named pipe, the first call to Copy will copy the contents.
            // The time to copy that data may well be longer than it takes to generate the events.
            // However, subsequent calls may copy nothing, but that does not do any harm.
            io.Copy(f, p)

        case notify.Remove:
            // Some user or process has removed the named pipe,
            // so we have nothing left to read from.
            // We should inform the user and quit.
            log.Fatalf("Named pipe '%s' was removed. Quitting", pipePath)
        }
    }
}

当没有写入程序时,命名管道读取器将收到EOF。此代码之外的解决方案是确保始终有一个writer进程保存文件描述符,尽管它不需要写任何东西。

io.Reader

for {
    err := io.Copy(&buff, fpipe)
    if buff.Len() > 0 {
        buff.WriteTo(f)
    }

    if err != nil {
        // something other than EOF happened
        return
    }

    time.Sleep(100 * time.Millisecond)
}

问题:当“最后一个编写器”关闭管道时,即使稍后可能会出现新的编写器,也会得到EOF。

解决方案:自己打开管道进行写入,不要关闭。现在,您可以将读取端视为永无止境的读取,而不会获得EOF。将以下内容直接放在打开管道阅读的位置之后:

nullWriter, err := os.OpenFile(pipePath, os.O_WRONLY, os.ModeNamedPipe)
if err != nil {
  logger.Crit("Error opening pipe for (placeholder) write", "err", err)
}
defer nullWriter.Close()